Pipes can be metal tubes internally lined with a thermoplastic tube of limited permeability, or flexible pipes comprising for example the following elements:
a frame made of interlocked steel tape intended to prevent collapse of the pipe due to the differential pressure between outside and inside, PA1 an inner sealing sheath made of a plastic material intended to provide inner sealing of the pipe, PA1 at least one layer of metal armours to withstand compressive and/or tractive stresses, PA1 a second external sheath made of a plastic material providing external sealing of the pipe. PA1 Charges comprising metal oxides: EQU PbO+H.sub.2 S.fwdarw.PbS+H.sub.2 O (1) EQU ZnO+H.sub.2 S.fwdarw.ZnS+H.sub.2 O (2) PA1 Charges comprising amines such as alkanolamines or polyethylene polyamines: PA1 Charges comprising alkaline or alkaline-earth oxides: EQU CaO+H.sub.2 S.fwdarw.CaS+H.sub.2 O EQU CaO+CO.sub.2 .fwdarw.CaCO.sub.3 EQU Ca(OH).sub.2 +CO.sub.2 .fwdarw.CaCO.sub.3 +H.sub.2 O.
The problems inherent in transportation of fluids at high temperature and pressure are linked with the permeability of plastic sheaths. It is well-known that the flow of gas through the thermoplastics used for manufacturing sealing sheaths increases with the temperature and the pressure. In the case of corrosive gases, such as H.sub.2 S, the metal armours or tubes can undergo accelerated corrosion. Furthermore, in the case of a flexible pipe, the gas can accumulate between the two sheaths, which can lead to bursting of the external sheath when the external sheath is less permeable.
Document EP-0,225,901 describes an inner sheath whose permeability is reduced by spiral winding of a fine metal strip around a plastic sheath. However, the areas of superposition of the strips remain very gas permeable areas.